Surgical Management of Moyamoya Disease

Moyamoya disease (MMD) is a rare cerebrovascular disease which is characterized by bilateral progressive steno-occlusion of basal cerebral arteries with emergence of coexisting abnormal net-like vessels.1 MMD is most frequent in Asian countries with an incidence ≤0.94/100 000, but an increase in incidence has been reported in non-Asian countries with some ethnic differences in disease characteristics.2–4 MMD shows worldwide a bimodal age distribution with a peak each in childhood and adulthood2–4; thus, it is one of the leading causes of stroke in children and young adults. The most frequent initial symptom of MMD adults in Asians and whites is intracranial hemorrhage because of fragile blood vessels and ischemic events, respectively.2,3 Children with MMD worldwide frequently experience ischemic events.2–4 The diagnostic workup includes magnetic resonance angiography or digital subtraction angiography and hemodynamic assessments using (semi) quantitative techniques, such as SPECT or PET.2 Historically, disease severity has been classified by the angiography-based Suzuki classification. This classification, however, neither correlates with disease severity nor allows therapeutic risk stratification and thus, has not been applied in routine clinical setting. As a consequence, the Berlin Moyamoya Grading has been established using standard diagnostic tools: magnetic resonance imaging and functional cerebrovascular assessment of hemodynamic impairment.5 This novel grading system correlates with disease severity and more importantly, allows to stratify the individual risk of surgical therapy. Only recently, the Berlin Moyamoya Grading has been validated on an independent Japanese data set.6 Cerebral hemodynamic impairment and repeat ischemic symptoms have to date been the main indications for treatment.2 However, because asymptomatic moyamoya is a progressive disease with an annual stroke rate of ≤13.3%,7,8 treatment indications for asymptomatic patients are currently revisited by the prospective AMORE trial.8 For …